A Review of “Iconic Memory Requires Attention” by Persuh, Genzer, & Melara (2012) By Richard Thripp EXP 6506 – University of Central Florida September 3, 2015
Introduction
In Introduction What is iconic memory? A preattentive store of visual information, such as letters, digits, colors, shapes, orientations, etc. (p. 1).
In Introduction Two paradigms: • Partial-report • Cued change detection task This study uses both .
In Introduction Partial report requires the subject to report what was different between two conditions — in this study, it was used in Experiment 2, where the subjects were asked “V or H” in respect to a rectangle being vertical or horizontal.
In Introduction Cued change detection requires the subject to report whether (or not) there was a change between two conditions — it was used in Experiment 1 in this study.
In Introduction “People frequently fail to notice change between two visual images, even when the change is relatively large ” (p. 1). Possibly due to capacity limitations (Rensink et al., 1997), a disruption of iconic memory (Sperling, 1960), etc.
In Introduction In partial report conditions, subjects often say they cannot remember all the items on the display, even though they see all of them. In Sperling’s original work (1960), this was reflected in much lower performance in the whole-report condition than partial report.
In Introduction Spatial attention and the “neural correlates of visual awareness” function independently (p. 2). This implies that much of what we attend to never reaches conscious perception.
In Introduction Block (1990, 2005) proposed a distinction between: • “ Phenomenal ” consciousness – detailed and perhaps limitless in capacity • “ Access ” consciousness – “ limited to the ‘ consumer ’ information residing in the brain’s systems …” ( Persuh et al., 2012, p. 2)
In Introduction Several prior experiments have supported the phenomenal / access distinction. However, none have manipulated attention . The purpose of this study was to add attention to the model, possibly clarifying whether attention is needed to create iconic representations.
Materials and Methods
Materials and Methods TWO (2) experiments!
Materials and Methods EXPERIMENT ONE Participants (p. 2): 24 undergrad students, 12 male, 12 female Ages 18-32 ( M = 19.3) City College of the City University of New York Normal or corrected-to-normal vision and no head trauma or psychiatric or neurological illness
Materials and Methods Apparatus for BOTH experiments (p. 2): 16” CRT monitor (Sony Model G220) 100 Hz refresh rate (refreshes every 10 ms) This monitor is often used in studies of this type.
Materials and Methods Experiment ONE: Two types of tasks (p. 2): Visual search task (easy and hard) Change detection task FIVE CONDITIONS, initially presented in a specific order to assess subjects’ baseline abilities.
Materials and Methods 1. Change detection task (200 X) 2. Easy visual search task (200 X) 3. Hard visual search task (200 X) 4. Change detection AND easy visual search (400 X) 5. Change detection AND hard visual search (400 X)
Materials and Methods • Trials were presented in blocks of 50 with short breaks in between. • Only ONE condition was used in each block. • 28 blocks and 1400 trials were conducted (per subject) . • Blocks 1-3 were single-task, blocks 4-5 were dual- task, and blocks 6-28 alternated (counterbalanced).
Materials and Methods • The circles and rectangles were shown in all 5 conditions. However, frames 4-6 from Figure 1 were omitted in conditions 2 and 3 (visual search alone). • No time limit was placed on the final response in any of the trials.
Materials and Methods 1 . Change detection involved the participants detecting a change in orientation (vertical or horizontal) in 1 of 8 darker rectangles on the monitor.
Materials and Methods 1 . Following a 200 ms display of the rectangles in their initial position, a yellow line cue was shown for 100 ms, followed by 900 ms of “silence,” and then 250 ms of the rectangles in their final position, with the subject then being asked whether the rectangle in the position of the yellow line changed orientation (or not). (None of the other rectangles were eligible to be changed.)
Materials and Methods 2 . The easy visual search involved noticing whether one of the 8 white circles near the center of the monitor had a white bar attached to it. In this condition, subjects were then immediately asked, “Did you see the target?” (Recall that the circles were displayed continuously for 250 ms, with rectangles appearing in milliseconds 51-250.)
Materials and Methods In the “visual search alone” conditions (2 and 3), the monitor immediately displayed “Did you see the target?” after the circles were shown— the three other frames (100 ms with yellow cue line, 900 ms “silence,” and 250 ms rectangles) were omitted .
Materials and Methods 3 . The hard visual search was like condition 2, but involved noticing whether one of the 8 white circles near the center of the monitor did not have a white bar attached to it (while at least 7 circles did). In this condition, subjects were then asked, “Did you see the target?”
Materials and Methods 4 . The change detection AND easy visual search condition involved a combination of conditions 1 and 2, where subjects were asked “Change?” OR “Did you see the target?” at the end of each trial, without foreknowledge of which question would be asked.
Materials and Methods 4 . This means subjects were asked to simultaneously attend to BOTH the circles (visual search) and the rectangles (change detection), with no extra time given.
Materials and Methods 5 . The changed detection AND hard visual search condition involved a combination of conditions 1 and 3, and was identical to condition 4 except for the search task involving determining if a circle did not have a white bar attached to it. This was, by far, the most difficult condition.
Materials and Methods In both dual tasks, the search prompt appeared with probability 0.6 (and the change detection prompt with probably 0.4), “to ensure that performance on the search task was maintained” (p. 3).
200 ms = 1/5 second Possibly the amount of time it takes to pronounce the first syllable of “Mississippi.”
50 ms = 1/20 second One frame in a motion picture: 1/24 second (41.667 ms) A typical LCD monitor has a 1/60 second (60 Hz; 16.667 ms) refresh rate The monitor the experimenters used was a 16” CRT (cathode ray tube) Sony G220 monitor with a 1/100 second (100 Hz; 10.0 ms) refresh rate
Materials and Methods Click here for an animated GIF similar to Figure 1, recreated by Richard Thripp. The timing may not be rendered with precise accuracy, but should give you a rough conceptualization of the experiment.
Materials and Methods Because the results of Experiment 1 were “ extremely robust ,” the authors “elected to test relatively fewer participants in Experiment 2” (p. 3) – ¼ the participants – 6 instead of 24 . No participants in Experiment 2 participated in Experiment 1.
Materials and Methods EXPERIMENT TWO Participants (p. 3 – 4): 6 (!) undergrad students, 3 male, 3 female Ages 20 – 33 ( M = 24.7) City College of the City University of New York Normal or corrected-to-normal vision and “neurologically normal” (note: head trauma and psychiatric illness were not addressed)
Materials and Methods EXPERIMENT TWO was identical to Experiment 1, except for: • 1) The introduction of a checkerboard pattern mask displayed for 50 ms over the search array after the display of circles and rectangles (p. 4). The purpose of the mask was to interrupt the potentially persisting iconic image.
Materials and Methods EXPERIMENT TWO was identical to Experiment 1, except for: • 2) Change detection was replaced with partial- report — a cue appeared for 200 ms and subjects were then asked “V or H?” with regard to the orientation of the previously displayed rectangle at the cue location (p. 4).
Materials and Methods EXPERIMENT TWO was identical to Experiment 1, except for: • 3) Dual tasks required attending to both circles and rectangles as before, with the task indicated immediately after the pattern mask (p. 4).
Materials and Methods The purpose of experiment 2 was to address several possible alternate explanations that could be provided for the results from experiment 1 (p. 5).
Results
Results Experiment One: Accuracy for easy visual search alone: M = 98.88%, SD = 2.59% Accuracy for hard visual search alone: M = 69.40%, SD = 5.54% Accuracy for change detection alone: M = 87.85%, SD = 5.90%
Results (E (Experiment One)
Results Accuracy during dual tasks was identical for both easy and hard visual searches! However, it was highly significantly different with respect to change detection…
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